This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In creation and distribution of pictures and videos, it is known to produce a first original video for a specific original display having original viewing conditions. In the following, viewing conditions include both the display on which the content is rendered and the environment of the rendering. Thus viewing conditions can include the color gamut of the display, the maximum luminance of the display, but also ambient light falling on the display, the luminance and chromaticity of the background, the adopted white of the human eye, the viewing distance, or the temporal evolution in any of those conditions.
It is further known, that the creator of the video produces a second, reference version of the video that is well adapted to be displayed on a reference display having reference viewing conditions that are different from the original viewing conditions. This reference video may be generated either by manual color grading or by color processing such as gamut mapping and tone mapping or a combination of manual color grading followed by color processing.
However such mentioned reference video is of fixed nature in the sense that it contains colors that should be shown under reference viewing conditions. If the viewing conditions are different from reference viewing conditions, the reference video does not show up correctly. For example, neither the reference video nor the original video can be displayed on a target display having target viewing conditions that are different from both the original and reference viewing conditions. Indeed, target viewing conditions depend on end-users displays having various different characteristics (e.g. different color gamut, different black levels, different peak luminances, different maximum full frame luminances, bit depth, etc) since based on different technologies (LCD, OLED, LCD with LED backlight, LCD with Quantum dots layer, . . . ) and/or different architecture (TV set, smart-phone). Target viewing conditions further depend on the specific application, for instance a version of video content adapted for viewing in theaters may be perceived very differently if the same version is played in other viewing environment such as in home with a DVD or Blu-Ray player.
Consequently, the end-users display when displaying either the original or the reference video fails to preserve the artistic intent of the colorist because some colors, as specified by the colorist, in the original or reference video may not be preserved during display.
A solution to solve this issue is to use adjustable color mapping operators, such as tone mappers and color gamut mappers, to create a new version of the video that is adapted to target viewing conditions as shown in FIG. 1. Such tone mapper is for example described by Erik Reinhard in his book entitled “High dynamic range imaging” published by Morgan Kaufmann in 2006 (chapter 6). However, those operators have poor performance for example with respect to adaptation to local image regions, or with respect to adaptation to specific light situations, or with respect to dark, medium or high colors, or with respect to specific semantic objects such as human faces. Indeed, since the performance of those operators is not acceptable, creators prefer to generate different video versions by manual color grading that will take into account the specific reference viewing conditions.
Other solution is disclosed into EP2498499 A1 wherein a first image data depicting the image associated with first gamut and second image data depicting the image associated with second gamut are interpolated into output image for display on a target display associated with a target gamut wherein the interpolation parameters are directly derived from the target gamut and from gamuts associated with the first and second image data. Similarly EP2667378 A1 discloses that first images in a first version of a particular image targeted for a first class of display and second images in a second different version targeted for a second different class of displays are interpolated to obtain third images being targeted for a third class of displays wherein the interpolating may change for clusters inside the images. However as for adjustable color operators, such solution fails to cope with a high range of adaptation to viewing conditions and to cope with image details.
A method for generating a new color video adapted to target viewing conditions from existing color videos adapted to other viewing conditions is therefore desirable where the method is capable of keeping a high range of adaptation to viewing conditions that existing color mapping operators cannot achieve.